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Welcome to the number mines of Digitopolis, the famous kingdom from The Phantom Tollbooth! This fall, we hosted a table at Princeton University’s annual Community & Staff Day event. Big crowds meant that we needed something simple, but we wanted to be creative too. Since we had successfully offered the number mines at a massive math event last spring (you can read about it here and here), we decided to bring them back for more numerical fun.

Alas, the original number mine (which was artfully constructed by the Arts Council of Princeton) wasn’t salvaged after the math event. This meant that Katie and I had to build our number mine from scratch. The first part of this post describes how we ran the event table. The second part describes how we build the mine.

At the event, kids would reach into the number mine and pull out a plain wooden number. I bought the numbers online from Woodcrafter, where they range in size, thickness, price, and font. I got the 4″ numbers that were 1/8th of an inch thick. Each number cost 56¢.

We found that 4″ was a great size for decorating, but if 56¢ per piece is outside your budget, you can go smaller. A 1″ number of the same thickness, for example, costs 23¢. Or, if you want to go even cheaper, skip the wood and print your numbers on white card stock. We loaded the numbers into the mine, and the kids “dug” them out with their hands.

Once kids found a number they liked (7 and 8 were very popular), they went over to the number decorating area, which was stocked with metallic makers, glitter markers, small gemstones, and glue. We had a relevant quote from the book on display too. Kids really got into decorating. One little girl spent 25 minutes working on her number!

Note! If you use squeeze glue (as opposed to hot glue) make sure to have paper towels or small paper plates handy so families can safely transport their numbers home. Hand wipes are also a good idea for sticky fingers and tabletops. Katie and I dressed for the occasion in miner’s helmets and safety vests.

So, that’s our event table…now for constructing the mine! You certainly don’t have to get as elaborate as we did. You can create a mine by covering a box with grey paper. Cut a hole in the box’s lid, throw some numbers in there, and have kids reach into the box! Or you could skip the mine altogether and just do the number decorating part of the project. But if you do want to build a mine, here’s how we did it.

STEP 1

Find a big, flat box that isn’t too deep. You don’t want kids to have to reach too far down for the numbers – especially the little ones. We used a 34″ x 54″ inch box lid, and then attached 6 photo storage boxes to the bottom using hot glue and packing tape. This resulted in a mine that was 5″ deep. Here’s a shot of the underside.

Since the box lid didn’t reach all the way to the bottom of the photo storage boxes, we closed the gap by attaching big strips of corrugated cardboard to 3 sides of the mine. We left it the mine open in the back so we could restock numbers during the event.

STEP 2

Cut holes in the top of the box. We found it helpful to draw the holes before we started cutting. That way, we could be sure we weren’t cutting into any of the support boxes and we knew that the numbers would fit through the holes.

STEP 3

Create the rocky, craggy landscape of your mine. We bunched up big pieces of black bulletin board paper and attached them to the box with masking tape (you might recognize that texture from this Instagram pic).

STEP 4

Now for the really, really messy part. Papier-mâché. We don’t have a sink in our work space, and the nearest bathroom is far, far away. So we wanted to create the smallest mess possible. In other words, we didn’t want to cook, mix, or blend any sort of papier-mâché paste (or dilute any glue). After a little research, we settled on liquid starch.

Below are our tools – 2 enormous jugs of liquid starch, 2 plastic roller trays, and 4 paint brushes (the bristle brushes worked better than the foam ones). Oh, and we also put a plastic tarp under the mine so we wouldn’t ruin the table.

Since we had a lot of area to cover, we used big, 6″ x 16.5″ pieces of newspaper. Occasionally, we use a smaller strip for edges or crevices, but mostly we stuck with the big ones.

The liquid starch held up well! It did coat our hands with sticky residue that required multiple rounds of soap and scrubbing to remove, but it wasn’t too bad. Honestly, the worst thing about the liquid starch was the fact that it was scented. “Mountain Fresh” scent to be exact. Hoo boy. You could smell the mountains the minute you took the cap off. After a couple minutes, the fragrance was looming in the room like a big, ominous fog. Katie put together a little graphic to convey the overpowering Mountain Freshness.

We left the first layer to dry overnight. For the second layer, we got a little experimental. While researching liquid starch, we learned that some people absolutely rave about using white paper towels and computer printer paper for papier-mâché projects, especially if the projects are going to be painted later. So we decided to give it a try. We papier-mâchéd the bottom of the mine with paper towels, and the top portion with computer printer paper.

Wow, did the paper towels suck up the liquid starch! The printer paper needed much less. But the printer paper was so stiff, it created unwanted gaps like this one:

The solution was to drape a liquid starch-soaked paper towel over it. Below is that same gap with the paper towel over it. As you can see, the soft paper towel completely obscures the gap. I didn’t officially test this, but I believe newspaper would obscure gaps as well, perhaps even better than the paper towels.

I was a little worried the paper towels were too transparent. But overnight, they magically dried to solid white.

In the above photo, you can see there were still wet patches in crevices where the liquid starch had pooled. Katie hit those with a hair dryer, no problem. And we should add that, even now, things were still smelling quite Mountain Fresh.

STEP 5

Time to paint! We used this awesome textured-stone effects spray paint by Valspar. It’s fun, but pricey ($10 a can at Lowe’s). Our mine required 3 cans.

A cheaper option would be to use gray paint to cover the mine, then dab on darker gray with a piece of sponge. This will get you a textured surface, without the hefty spray paint price. Once the spray paint had dried (which, we might add, finally dissipated the Mountain Fresh fragrance), we decorated some numbers and attached them to the mines with hot glue. We hot glued some large plastic gems on as well – purchased from the wedding favor aisle at Michaels Craft Store.

And this, dear readers, is when we discovered the fatal flaws in regards to paper towels:

When dry and spray painted, paper towels become incredibly brittle. I poked a hole right thorough one section while merely tapping on it (we eventually covered the hole with the number 8).

The texture of the paper towel absolutely comes through in the end. So if your paper towels have little hearts embossed on them, you’re going to see little hearts under the paint.

The edges of the paper towels are clearly defined. Unlike the newspaper and the printer paper, you can definitely see the edges of the paper towel under the paint. So our rocky surface looked like, well, draped paper towels. You could even see the dotted perforations that separate the paper towels.

The printer paper, on the other hand, was much sturdier and the edges were hidden under the paint. The lesson? DON’T use paper towels for papier-mâché projects. Use newspaper and printer paper instead. In fact, I highly recommend printer paper for the second layer of painted papier-mâché projects. Very sturdy, holds paint very well.

However, paper towels are what we used and their brittle weakness made me and Katie very, very nervous. We were positive that kids were going to put their hands right through the mine as they leaned in to select numbers.

Anticipating trouble, we brought duct tape and a couple of step stools to the event. The stools elevated the kids right up to table level, allowing them to keep their weight mostly on the stools and not on their hands. So the paper towels held, but there were a couple time you could see them bending. Katie and I would brace ourselves for a tearing, crunching, breaking sound. Thankfully, it never happened. Whew!

This paper disappears in water before your very eyes, leaving the letters floating free. It’s the ultimate aqueous word scramble!

I was very intrigued when I spotted this dissolving paper in Educational Innovations’ online catalog. I’ve certainly seen the floating letter experiments with Skittles and M&Ms, but I’ve never seen anything like this paper! It’s made of sodium carboxyl methyl cellulose, a non-toxic substance that dissolves quickly in hot or cold water. Each sheet is 8.5″ x 11″. You can buy the sheets in packs of 15 for $7.95, packs of 30 for $13.95, or, if you want to vanish a whole novel, you can get 100 sheets for $42.50.

The paper is about half the thickness of standard office printer paper, but it went through both of our office printers and the copy machine with no tearing or jamming. Granted, I was just printing 1 sheet at a time. I did try 3 pages in a row on our most trustworthy office printer. Unfortunately, it had trouble grabbing the thin paper and actually missed the final sheet of the print job entirely. I was waaaay too chicken to try multiple sheets in the copy machine.

The product description stated that this paper works with “most laser printers and copiers.” But we took it a step further and also tested an inkjet printer, Sharpie permanent marker, roller ball pen ink, and ballpoint pen ink.

First, the laser jet printer. I filled a dish tub with a couple inches of room temperature water a dropped the paper in. It floated for a just moment, and then started rapidly dissolving. In a few seconds, it was reduced to a thin, almost transparent, paper-shaped film.

The package recommended giving the water a gentle stir, so I poked a drinking straw in the solution. It started breaking up, dissolving further, and yes! The letters started floating! How long do the letters remain on the surface of the water? A long time! I left them in the dish tub overnight, and they were still happily floating the next morning.

Second test, copy machine. The letters printed considerably lighter on the page (this was a toner thing with our copier, not the paper). But that didn’t impair the letters from floating on the water like little alphabet ducks!

So our laser jet printer and the copy machine worked. What didn’t work? Our inkjet printer. First of all, it blotted the paper during printing…

And when it came to the water test, the letters just disintegrated:

The same applies for Sharpie permanent marker:

Roller ball ink and ballpoint ink also broke apart. The ballpoint ink shredded immediately (you can just see the sentence “Will ballpoint pen work?” at the bottom of the image below). Roller ball, I am surprised to report, held out a little longer.

It was sort of cool. The roller ball ink blurred, sunk a little, and then just hung in the water (which is when I snapped this Instagram pic). Eventually, however, the roller ball ink went the way of the ball point, Sharpie, and inkjet. It dissolved into a black smudgy mess.

It’s important to note that for all of these tests, the paper didn’t dissolve entirely. There was a little cloud of solution that started hanging around the bottom of the dish tub. The more paper I dissolved, the cloudier the water become. So if you’re going to do this with a bunch of kids, you will definitely need to change the water every so often.

Finally…

Being the incredibly mature people that we are, we decided to test the paper in the toilet. It worked. Of course it worked.

But no matter where you’re dissolving this paper – a dish tub or a commode – the letters do float apart very quickly. So leaving a secret message for someone isn’t really going to work (unless they’re standing right next to you and reading quickly). But this would be a fantastic way to introduce the concept of the anagram. Or jump-start a discussion about biodegradable materials. Or, just experience the fun of watching a sentence you’ve written slide apart and swirl across the surface of the water. Magic!

Recently, while in Brooklyn, I wandered into a little toy store called Matt & Juliette. There, I discovered some neat-o wind-up butterflies by Seedling. The clerk at the toy store explained that some people like to put the butterflies inside birthday cards. When the recipient opens the card, the butterfly flutters out. If it works for cards, I thought, it’ll totally work for books! I immediately purchased a pair to test out. They retail for $3 each and come in 4 different colors and styles.

As you can see, the toy is pretty simple. You hold one half and twist the other half. This motion winds the 2 rubber bands, which ultimately propel the toy skyward.

The directions warned that winding the rubber bands too tightly could cause them to snap. This is true. Over the course of 20 test flights, we broke 2 rubber bands. But there are two spare rubber bands in each package, so no problem! Alas, one of the plastic hooks on the smaller butterfly snapped within 5 minutes, rendering the toy useless, but the other one held out just fine. Ready to see a butterfly in action?

There’s no denying it. It’s fun to have a butterfly sail out of a book. But the toy is erratic. Sometimes it flutters around the table, sometimes it dives to the floor, and sometimes it tears out of the book and zooms away like a bird.

There is absolutely no way to predict, or manipulate, the butterfly’s path out of book. Especially when it decides it wants to attack you.

The erratic flying made me wonder if this toy would freak out kids. So I tested it out on my unsuspecting children (ages 5 and 7). They loved it! There was no flinching or shrieks of alarm when a butterfly suddenly flew out of the book. In fact, they took turns winding it up and releasing it from their hands. This made me realize that the toy is a simple machine, and might work at a STEM program too.

In short, for $3, this is an inexpensive piece of magic for your next story time or program. Just make sure to buy extra butterflies in case the plastic breaks. Happy flying!